There have hitherto been systems using sunlight or wind force as a renewable energy source to generate electric power. Sunlight may significantly be available only in a sunshine duration and not so in a cloudy or rainy weather. Wind force power generation utilizes a current of air where there is a calm and which is basically small in density. Hence, these systems tend to be made in a large size. In contrast, the use of wave power in the ocean where there are seawater waves of large momentum having a wave height, e.g. of 1 to 2 meters always, is proposed as preferred to achieve or activate power generation in a smaller system size and an enhanced efficiency. Thus, there have heretofore been proposed a number of wave activated electric power generating systems to convert the kinetic energy of waves such as in the ocean into electrical energy. For example, there is known a power generating system in which wave force energy is converted into air energy to drive an electric generator via an air turbine. It is provided with an air chamber which vertically bends a horizontal water conduit, an air tank connected to the chamber and further a duct that communicates the tank with the atmosphere such that the turbine is rotationally driven by the air current in the duct (see Patent Reference 1). Since large energy of water waves is used only in the system to compress an identical volume of air which is small in momentum, the system needs to be made of a large size and must moreover be low in energy conversion efficiency.
There is also known a seawater turbine electric power generating system in which a floating body is moved vertically up and down with seawater waves, a piston connected to the floating body is vertically moved up and down in a cylinder, and seawater in the cylinder is fed into an air chamber both when the piston is moved up and when the piston is moved down (see Patent Reference 2). While there tends to be lack of uniformity in the flow of seawater fed to the air chamber from the cylinder, air in the air chamber acts as a cushion so that the lack of uniformity may sufficiently be removed to allow electric power to be generated stably. While this system in which the use of a seawater flow of large momentum increases the conversion efficiency, needs to securely connect the cylinder for supporting the piston moving vertically up and down and connect it to a bottom of the sea or to a quay wall, it has a problem of its durability.
There has hitherto also been known a wave activated electric power generating system comprising a floating body so formed as to be moored and shaped in the form of a long cylinder, an electric generator with which the floating body is provided, a ballast mounted to a lower end of the floating body, a buoyancy adjusting chamber disposed in a middle region of the floating body and at a position remote from the ballast, the buoyancy of the buoyancy adjusting chamber being adjusted to cause the floating body to be floating vertically, an air chamber disposed at an upper end of the floating body, an upper part of the floating cylinder body being made less uneven to reduce water resistance to vertical movement of the floating body, a protrusion provided at a lower part of the floating body to increase water resistance, an air turbine utilizing an air current produced by the vertical movement of the surface of water between the inside and outside of the air chamber, and an electric generator disposed at an upper end of the floating body for rotational driving by the air turbine (see Patent Reference 3). In this system, it is assayable that the unit need not necessarily be secured to a bottom of the sea or a quay wall, that adjusting the buoyancy of the buoyancy adjusting chamber disposed in the middle region of the floating body makes the unit floating on the sea and the floating body is provided with a protrusion that makes the floating body less liable to move against the undulating motion of waves. However, converting the energy of seawater waves having large momentum to the air current of small momentum to activate power generation with an air turbine leaves the conversion efficiency low. Further, shaping the floating body in the form of an elongate cylinder leaves the problem unsolved that a severe rolling may be caused by a side wave in a violent storm such as of a typhoon.
There has hitherto been also known a wave activated electric power generating system using a tightly sealed buoy and an oscillator connected via a spring to an inner wall of the buoy and in which motion of the oscillator relative to the buoy floating on the waves in the ocean and vertically oscillating is utilized whereby an electric generator secured to the oscillator is rotationally driven with a pinion in mesh with a rack (see Patent Reference 4). In this system, the electric generator is stored in the tightly sealed buoy and protected from seawater and the structure is well durable. It is, however, necessary to adjust the resonance frequency between the spring and the oscillator. Since the resonance frequency varies with a load for power generation, stable oscillations can hardly be obtained. With a rolling by waves, the buoy tends to incline, bringing about the problem of changes in resonance frequency of the electric power generating system and a lowering of power generating efficiency.
There has also been known heretofore a wave activated electric power generating system having a floating body vertically moving up and down with undulations on the surface of the sea and in which electric power is generated using a backing movement produced at a portion of rotary shaft fitted in a bearing of the floating body and having a mooring member for connection to and mooring via a wire rope an anchor placed on a bottom of the sea (see Patent Reference 5). This requires a part of mooring to be installed on a bottom of the sea and involves a problem of its construction and selection of a site of installation. There has also been known heretofore a wave activated electric power generating system in which an undulation of waves is converted into a vertical up and down movement of a float (or ship) and utilizing the principle of a leverage for an undulation of waves, compressed air is produced by a hydraulic unit and utilized to operate a turbine electric generator (see, for example, Patent Reference 6). In this system, the leverage is hard and long, increasing the distance up to a position where the turbine electric generator is secured, giving rise to the problem of durability, such as of making a part liable to break by a storm such as a typhoon.
There has also been known heretofore a wave activated electric power generating system (see Patent Reference 7) in which a linear electric generator as the wave energy converter is provided in a floating member as the buoy and including an elongate support structure in the form of a vertically oriented column having a submerged member provided below an average draft line, the support structure being vertically oscillated with waves with respect to the floating member to operate the linear generator, taking out electric power into the outside. In this system, since the submerged member is preferably not moved with the waves, the rotary electric generator is placed in the submerged member. A tension mooring system is utilized comprising a cable extending to a balancing means adapted to be suspended from the submerged member via a pulley mechanism 54 from a ballast means 52. There has been a proposal to make the submerged member less liable to move with the waves by utilizing an electromagnetic brake of the rotary electric generator operated when it is varied vertically to cause an electric current to flow through an electric load. It has also been proposed preferably to use a battery. In such proposals, however, it is the function of the rotary electric generator to make the submerged member less liable to move. It is by the linear electric generator mounted in the floating member that electric power is generated for taking out outsides. It is mostly the floating member that is vertically oscillated with the waves. The submerged member, which is at all underwater and made by water resistance less liable to move and is further made less liable to move by using the electromagnetic brake of a rotary electric generator whose quantity of electric generation is small at all. Furthermore, the rotary electric generator which is arranged stored in the submerged member and dipped in seawater, have given rise to the problem of its durability and electrical leak.
There has hitherto been also known a wave activated electric power generating system (see Patent Reference 8) in which the wave energy converter has a tetrapod (trade mark) or wave-dissipating concrete block placed on a bottom of the sea and connected to one end of a chain of short link whose other end has a weight attached thereto, the short-link chain being engaged with a sprocket with which a float is provided whereby the float moving up and down simultaneously as the surface of the sea is up and down turns the sprocket, to rotate an electric generator and in which a reversible unit is provided to rotate the electric generator unidirectionally. The reversible unit is complicated, has low efficiency and may cause a failure. The short-link chain extending in seawater tends to have living things such as shells in the sea, seaweeds and other foreign matters attached thereto, preventing its engagement with the sprocket. Further, the problem arises that a large shake of the float and the short-link chain in raging waves in a storm such as a typhoon may cause the weight to move largely, disengaging the sprocket from the chain.